First Test: 2009 GMC Yukon 2 Mode Hybrid

Green Giant: Big technology in a Big SUV (with big stickers) may not be enough

Truck Trend, March 12, 2008

Although they'd never admit it, the folks at GM learned a thing or two from Toyota. Not only did the Prius give Toyota a "greener" public image, it did a good job with the technology, too. Now, it's GMs turn to shine. We recently got some time behind the wheel of a 2009 GMC Yukon 2-Mode Hybrid (on sale now, along with the Chevy Tahoe Hybrid) to see how it compares with a non-hybrid model. After just finishing up a 12-month, 20,000-mile tour of duty with a comparably equipped GMC Yukon SLT2 non-hybrid model, we can say the new 2-Mode system (co-developed by DaimlerChrysler, BMW, and GM) is nothing short of stunning. In large-SUV history, this just might be the single greatest leap forward in powertrain technology. So why does GM want to put such an impressive piece of technology in such an unpopular vehicle? The answer, says GM group V.P. of powertrains Tom Stephens, is simple: "This choice highlights our commitment to save as much fuel as possible by applying our best technology to the highest fuel-consuming vehicles first."

Whether GM's become a better corporate citizen remains to be seen, but given this is a fuel-gulping 5600-pound sled, the results are impressive. Recently released EPA fuel-economy numbers don't look stellar at 21-mpg city/22-mpg highway, but that's a huge jump up from a non-hybrid. Our comparably equipped long-term 5.3-liter V-8 GMC Yukon averaged 13.9 mpg combined (around 12 mpg city/ 18 highway). The same city routes in our Yukon 2-Mode Hybrid yielded 17.7 mpg with a combined average of 18.2 mpg over three tankfuls. In a world where O.E. designers and engineers are slashing and clawing for a fraction of a percentage point to improve fuel economy, a year-to-year jump over 30 percent (combined) is impressive. How does the system work?

At the heart of the 2-Mode system is the electronic variable transmission (EVT), which uses two 60kW electric motors that allow continuously variable operation at high and low speeds. Additionally, there are four fixed gears that also can act as a normal automatic when needed. Both are controlled by a computer with a sole purpose of making sure systems work together to provide the maximum operating efficiency based on vehicle load and driving conditions. Power for the two EVT electric motors comes from a 300-volt nickel-metal hydride energy-storage system, located under the second-row seats (which can flip and fold forward, though not electronically). The batteries are primarily charged during regenerative braking, but also can be charged while cruising. The hybrid powertrain uses the standard all-aluminum 6.0-liter Gen IV V-8 gas engine with active fuel management, which employs a new late-intake valve-closing technology, allowing the engine to run in V-4 mode longer and shut off sooner when coming to a full stop. Full electric takeoffs (depending on how you accelerate, up to 25 or 30 mph) are smooth and silent. Engine startups and shut-downs are noticeable but not intrusive, though getting used to the dead quiet at stop signs or traffic lights will take some time. (Now if only the Hybrid sticker packages-too many in too many places-were as seamless and subtle as the powertrain operation.)

GM included two separate readout strategies to provide the driver with instantaneous information: one analog gauge, one computer screen. The economy gauge teaches the driver (swinging needle) how to use the most efficient braking and accelerating techniques (in a nutshell, extreme smoothness rules the day). Similarly, a dedicated "Hybrid" readout on the nav screen identifies where the power is coming from (battery or engine) and where it's going (wheels or battery). Both are simple and easy to use.

Also included with this technology are a host of exterior changes designed to improve aerodynamics. Gone are the foglamp and tow-hook openings. The grille is slightly larger for better cooling. The roof rack rails are eliminated for less drag. Runningboards are tapered front and rear to decrease wind resistance. The previous round body shape was given sharper cuts to hold air, more shapely rear taillights cut through wind better, and a longer and wider front air dam moves more air underneath.